Verification of Appearance Failure in Application of Injection Foam Molding to Automobile Exterior Parts by Short Shot Method～Investigating the Mechanism of Dimple Generation～

There are appearance quality issues when applying foam molding to suppress rib sink marks on exterior components. While the gas counter pressure method has been established as a solution for swirl marks, it is generally believed that addressing dimples can be achieved by improving transferability to the mold. In foam molding using the short shot method under gas counter pressure conditions, it is desirable to increase internal pressure to suppress rib sinking and dimpling. To achieve this, we focused attention on the fillers added to polypropylene as foaming agents. We investigated the influence of fillers, rubber, and talc in PP on foaming and their relationship with dimples. As a result, we confirmed that rubber and talc as foaming aids have a synergistic effect in preventing bubble enlargement and refining bubbles. Furthermore, we found that in the GCP condition, bubbles are distributed directly beneath the dimple section and are absent in the surrounding area, indicating that dimples are caused by localized sink marks arising from bubble segregation. Based on these results, we summarized a formulation policy for future composite materials.